1. Field of the Invention
The present invention relates generally to methods and machines for stacking material, and more particularly, to methods and machines for stacking elongated planar members, such as sheets of lumber, plywood, or other material, into packages to facilitate subsequent shipping and/or handling.
2. Description of Related Art
The lumber industry, in particular, uses stacking machines (or stackers) to collect sheets (or pieces) of lumber, plywood, and other wood products into packages (or bundles) to facilitate bulk handling and shipping. Lumber is generally produced in lengths between 4′ to 28′, with thicknesses ranging from 1″ to 12″, and having widths that range between 2″ to 24″. After production, the lumber is generally gathered into layers (or courses) and then supplied to a stacker where it is formulated into packages that are typically approximately 16 to 30+ layers high and range from about 42″ to 96″ in width.
The stacking process requires robust machinery. It is also desirable to have a stacker that is capable of efficiently stacking the lumber at a very high speed. It is further desirable to have stacking machinery that is easy to maintain and that requires very little supervision or manual tuning during the stacking process. The longer the machines are kept up and running between down times and the less manual intervention that is required, the better the process efficiency. Greater efficiency results in increased production and enhanced profitability.
The industry is therefore in need of faster and more reliable methods and systems for stacking the materials that are to be bundled together. In particular, in sawmills and planer mills that manufacture lumber and other wood products, the speed of equipment that feeds conventional stackers has been increased, without a corresponding increase in the stacking speed. This results in bottlenecks and inefficiencies at the stackers.
Conventional stackers are generally unable to meet the high demands placed on them by current lumber feed systems. Typically, a package of lumber is formed in the stacker using a set of forks (or stacker arms) to raise a course of lumber from stacker chains. The arms are then extended to an area containing the accumulated courses. Once the course of lumber has been set on top of the stack, the stacker arms retreat to pick up the next course. This process is repeated until the desired number of courses have been set and a full package has been created. The package can then be bundled and shipped, or subjected to further processing.
U.S. Pat. Nos. 4,290,723 and 5,613,827, and Published U.S. patent application Ser. No. 20030031550, disclose various machinery and methods for stacking courses of lumber into packages. Unfortunately, none of these, or other known conventional stacker designs, are able to stack lumber at the high stacking rates required to keep up with the increased speed of present feed systems. Conventional systems, for example, are only capable of a maximum of about 15 cycles per minute for a single carriage stacker, and around 24 cycles per minute for a dual carriage stacker—not taking into account down time between loads being stacked and general inefficiencies of the infeed and outfeed systems of the stacker.
In addition, conventional stackers have not provided the ability to stack shorter courses of lumber at a faster rate. Typical infeed systems are often able to supply shorter courses of lumber at higher speeds, but, with no way to stack them faster, this higher feed capacity is wasted on conventional stackers. There are generally as many short lengths in a formulated layer of lumber as there would be longer lengths. This means that you have to stack 10′ long, 12″ wide pieces of lumber, produced at 120 pieces per minute, with 4 pieces per layer, at 30 layers per minute (120 pieces/4 pieces per layer) in order to keep up with the infeed system. This is in contrast to 20′ long, 12″ wide pieces that are produced at 60 pieces per minute, which would only need to be stacked at 15 layers per minute (60 pieces/4 pieces per layer). Mills therefore need to be able to stack about 30 courses per minute or more in order to keep up with the infeed of smaller lumber courses, and should also have very few timing and maintenance problems.